They're effectively the same process occurring to different degree. A high side is what you get when you arrive at a point of unrecoverable inflection in such a wobble.

Not sure that’s true. My understanding is the lowside happens when the tires lose traction while cornering so the bike skids along the road on its side with rider often beneath it (or hopefully behind it).

The highside happens when the bike is cornering in a skid but the tires regain traction but he angle of the bike is insufficient for the speed and the radius of the corner. This regaining of traction causes the bike to flip towards the outside of the corner, throwing the rider over the high side.

A death wobble happens on any road (ie not just when cornering) and you hit a bump that the suspension can’t recover from which also causes a deflection in the steering. The action of the bike attempting to gyroscopically self-correct, coupled with the rebound of the suspension causes the bike to go into the wobble from side to side (if the bike has a steering or suspension flaw). You eventually get thrown off the bike either side.

> They're effectively the same process occurring to different degree. A high side is what you get when you arrive at a point of unrecoverable inflection in such a wobble.

Simply not true? Lean a bike in a turn and jam on the brakes will give you a low side. No wobble.

Loss of friction holding the bike up through the turn. Went from static to kenetic.

I don't disagree, but I also didn't mention low sides at all so I'm unsure of what you're trying to express here.

My point is that a high side is what happens if you lose and regain rear traction, landing you in an unstable death wobble that immediately flings you out. It's possible to regain traction after losing it in a corner and not high side, you just get some wobble which you (more, the bike's suspension) can hopefully correct for. It's a matter of degree.

Nah. Incorrect. The wobble can happen when you’re 100% straight up and down. Highside needs a lot of yaw force to get the flick.

Well, yes. How 'high' the side is depends on many factors, but it's a gradient. A death wobble when going in a straight line happens to be relatively weak with regard to how much force the rider is ejected with should it fully destabilize / lose contact w/ the road in either direction, but you still get ejected in the same way.

As you increase wheel misalignment with the direction of travel (and speed), more energy goes into the fling. As you increase lean angle (more lean means more time for the wobble to accelerate you) the fling gets more violent on one side and less violent on the other (the 'high' and 'low' sides).

Hence, the observation that high sides are what happens when you enter a death wobble that is already past the point of stability.

Do you have sources to prove this?

I race motorcycles, I have a mechanical engineering degree and build race motorcycles, spent a lot of time researching motorcycle suspension dynamics to improve my systems and I think you’re basically making this up.

We can chat about it more, but I’d like to see your sources so I can see what you’re basing this on.

Prove what, specifically? I'm honestly unsure which part is a controversial enough claim as to require sources.

It seems trivial to me that in both cases a perpendicular force applied at the road acts to fling you, and that said force comes from wheel misalignment with the direction of travel.

Is that not the case?

Prove that the dynamic instability that causes a speed wobble is the same thing that causes a high side.

Here is an article on the physics of wobble:

https://en.wikipedia.org/wiki/Speed_wobble

A high side happens when the rear tire breaks traction at lean, and is no longer able to hold the arc it’s trying to turn on. The forces in the tire, suspension, twist and deflection in the swingarm and the frame of the motorcycle rapidly unload, and the bike turns around the z axis if x and y are the flat plane of the road surface. Then catches traction, and that z axis rotation and gyroscopic forces becomes a violent flick to stand the bike up straight.

These things are totally different.

> Prove that the dynamic instability that causes a speed wobble is the same thing that causes a high side.

This is a broader claim than the one I made.

> A high side happens when the rear tire breaks traction at lean, and is no longer able to hold the arc it’s trying to turn on. [...] Then catches traction, and that z axis rotation and gyroscopic forces becomes a violent flick to stand the bike up straight.

How much lean? And how much traction loss / for how long? What if there's just enough to where a high side doesn't occur and the bike/rider don't fly off? Will the bike instantly right itself with no overshoot, without any sort of steering column oscillation? If there is an oscillatory response, what do you call it? What do you call it as you gradually reduce the lean angle to 0?

At near 0 lean angle, is this oscillatory response meaningfully different from the oscillation of a speed wobble?

My understanding is that the highside always has that wobble. This is the tyre losing and then (fatally) regaining grip just before the crash. It’s the regain of traction that causes the vector of force that throws the rider over the highside.

This is the death wobble for people who don’t know. https://youtu.be/eoc1EM6yUSc

In this video the rider handles it perfectly and doesn’t crash but you can easily see how this has caused many crashes. As I understand it, it is a harmonic wobble that intensifies and is due to a flaw in the design of the rear suspension on some Harley Davidson models that they have chosen not to fix to keep the designs authentic. Make of that what you will.

Another terrifying variant on the “death wobble” is the “tank slapper”. This is typically caused by a flaw in the front steering (specifically having the steering geometry too vertical). Having the front forks close to vertical makes the bike handle very fast so is favoured by sports bikes however if the bike steers too quickly and hits a bump the steering will veer uncontrollably from side to side eventually causing the riders wrists to hit the sides of the petrol tank as the bike careers down the road weaving uncontrollably. The most terrifying part of all is slowing down makes a tank slapper worse so pretty much the only way it’s possible to recover from a tank slapper is to accelerate hard, get the front wheel off the ground and put it down straight. As a rider even thinking about the prospect of accelerating hard when in that situation makes me feel sick. Tank slappers are prevented by fitting a steering damper. I had a (crazy) friend[1] who bought a bike that was infamous for tank slappers[2] and then remove the steering damper to “see what would happen”. He had a tank slapper on the West Side Highway in Manhattan.

[1] Hi Kirat!

[2] Old Suzuki TL1000s

Accelerating enough to be always spinning the back wheel is also the way to avoid high-siders. Perhaps only very powerful bikes can do this predictably at any speed. It's the same technique as a speed way bike, but on bitumen and far higher speeds.

Mick Doohan was a master at this. https://www.youtube.com/watch?v=Bs0Kg-niVk8

On the 'supermoto' side of things: https://www.youtube.com/watch?v=6SXtaUQxsWk&t=27s

Yeah that controlled drift thing at speed is completely terrifying and amazingly skillful. Not for me, though. I was always taught to set up before the corner with the bike still vertical "in slow, out fast". I guess that's why on the one hand I could never be a racer but on the other hand I never crashed.

Mick had a much different body position than is standard now.

If you spin the rear while you’re hanging off like a current MotoGP rider, you’re going to get flung into the atmosphere.

I’m sorry but this is conjecture about how to save or prevent a highside, you shouldn’t actually try to put this advice into practice.

When you’re putting input into the bike at lean, it won’t wobble. The wobble is a progression that starts with a lightly loaded front tire, and every bike I’ve ridden with a good quick front suspension geometry will wobble in the right circumstance. A steering damper will kill the progression of a wobble, but if you’re accelerating the front can still give a wicked shake on a bike with a damper. Enough to loosen the front brake pads, smash thumbs, etc.

When racing, if you have a hill crest that you’re accelerating over and you set the front down after the hill, it’s common to get a good shake. You learn to ride through it.

Highsides are unrelated to tankslappers - it is a totally different concept, as discussed in another post. As stated in the article the highside is caused by rear breaking traction and then regaining it while the bike is crossed up, sending you either over the bars or skyward. My own recent highside (6 weeks ago) was caused by an engine seizure after a downchange from fifth in a third gear corner in qualifying. I had the bike leaned over, let out the clutch lever and because of the lean angle the bike rear kicked to the left, grabbed, kicked right and threw me over the bars. Well, so I was told - I do not remember the crash, waking up in the medical centre.

Highsides are particularly nasty, especially if you are knocked out so that you cannot control your crash and get rag dolled.

Glad that you are ok. Engine seizures/failures are a frustrating way to end a race.

For relative values of OK - right collarbone/shoulder/4 ribs, right knee ACL (fortunately micro tears, not snapped) and a traumatic brain injury (big bleed). I had lowsided the previous round after losing the front and that was fine, you slide along the track, controlling the fall and slide. In the last one was pitched head first into the track, knocked out and got severely rag dolled.

Maybe you should find a different sport...

Splashing about in reef breaks off the south coast is a lot a fun .. and water's soft, right?

https://youtu.be/xjHaFOGBPzk?t=144

( As a physics note, you don't often see a three lipped wave:

https://youtu.be/xjHaFOGBPzk?t=346

)

Ouch

You can highside by locking the rear, but the common highside you see on track is pushing the rear tire past its limit of traction, while having a heavy load on the rear suspension. As the tire breaks traction, the rear suspension unloads, the tire catches because the force the suspension was putting into the tire is gone and now it only has to support its grip, the rear suspension loads heavily now that the tire has grip and the spring reacts in the way you’d expect. Boing. The yaw angle induced is enough to fling the rider off. I’ve high sided off and then once the bike was free of me it just started riding straight. Happy it was free of the problem.

The rider into the video is putting some really ham handed inputs into the motorcycle. It’s not a wobble, bikes don’t “wobble” at lean, it’s a culmination of looking at the front wheel, forgetting where they are in the turn, surprising themselves about how close they are to the line, scaring themselves about the cliff edge, while being shocked about what the bike is doing. The person on the bike has stopped riding, the bike was riding them at that point. It’s a good example of someone way out of their depth on a capable motorcycle.